Action Points

People with type 1 diabetes might be misdiagnosed with type 2 diabetes in adulthood.

The study suggests that diagnosis of type 1 diabetes should be considered in any middle-aged patient with type 2 diabetes who does not show good glycemic control on rapidly escalating therapy, especially if patients are slim.

People with type 1 diabetes might be misdiagnosed with type 2 diabetes in adulthood, researchers suggested.

Published in The Lancet Diabetes & Endocrinology, a cross-sectional analysis reported that 42% (95% CI 39-45) of people with type 1 diabetes were diagnosed between the ages of 31 and 60, despite representing only 4% (n=537) of new diabetes cases diagnosed after the age of 30 in the cohort.

"It is typically considered a disease of childhood and adolescence, but can occur at any age," wrote Nicholas J. Thomas, MRCP, of the University of Exeter Medical School in the U.K., and colleagues.

"Identification of type 1 diabetes in adults older than 30 years is challenging because of the much higher prevalence of type 2 diabetes than type 1 diabetes in older adults (type 1 diabetes accounts for <5% of all cases)," and diagnosis-related errors can often occur when diagnosing type 1 diabetes later in life.

Utilizing the U.K. Biobank, the researchers identified a total of 13,250 of 379,511 (3.5%) unrelated people who were of white, European decent and diagnosed with diabetes between birth and age 60. Type 1 diabetes genetic risk scores, based upon 29 genetic variants, were determined for all individuals.

All people with type 1 diabetes (1,286) belonged to the "high genetic susceptibility" group, while an equal amount of individuals with type 2 diabetes were reported in the low (n=5,982) and high (n=5,982) genetic susceptibility groups.

Among those diagnosed between the ages of 31 and 60, the clinical characteristics of adult-onset type 1 were mostly similar to those diagnosed with type 1 diabetes between birth to age 30, including body mass index (BMI), insulin treatment at study entry, and incidence of diabetic ketoacidosis as a discharge diagnosis.

However, the clinical characteristics of those diagnosed between ages 31 and 60 were significantly different from those diagnosed with type 2 at this age (all comparisons P<0.001):

BMI: 27.4 (95% CI 26.7-28.0; type 1) versus 32.4 (32.2-32.5; type 2)

Insulin at study entry: 100% (100-100%) versus 16% (15-17%)

Insulin 1 year after diagnosis: 89% (86-91%) versus 6% (5-6%)

Diabetic ketoacidosis: 11% (9-14%) versus 0.3% (0.1-0.4%)

"Our findings alert clinicians that type 1 diabetes occurs often after age 30 years, but that it is difficult to detect because of the predominance of type 2 diabetes in older adults," the group wrote, adding that "diagnosis of type 1 diabetes should be considered in any middle-aged patient with type 2 diabetes who does not show good glycemic control on rapidly escalating therapy, especially if patients are slim."

The researchers highlighted that a diagnosis of type 1 diabetes in adulthood cannot be based solely on the patient's genetic risk score, since a large portion of those with true type 2 diabetes will also belong to the "high genetic susceptibility group," although a low genetic risk score can seemingly cross out the possibility of type 1 diabetes.

In an accompanying commentary, Jose C. Florez, MD, PhD, of Massachusetts General Hospital in Boston, praised the study, calling it an "ingenious application of genetics." Type 1 diabetes genetic risk score is "extremely accurate, will become inexpensive, and only needs to be tested once in the lifetime of an individual," he wrote.

However, he highlighted that the study failed to address LADA -- latent autoimmune diabetes of adults -- writing, "whether LADA is a distinct entity, a less aggressive form of type 1 diabetes on an autoimmune continuum, or an artificial construct that results from a mixture of patients with type 1 and type 2 diabetes remains a point of contention."

Florez also warned that "the outdated designations of type 1 diabetes as 'juvenile onset diabetes' and type 2 diabetes as 'adult-onset diabetes' reflect the incorrect categorical paradigm that has hindered the ability of clinicians to correctly diagnose outlier cases, causing unnecessary delays in instituting the appropriate therapy."

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